Ultrasonic surgical instruments may be used in medical procedures to, for example, dissect or cut living organic tissue. The dissecting or cutting action is accomplished by a surgical end-effector, such as a hook, at the distal end of the ultrasonic instrument. In an ultrasonic instrument, the end-effector cuts by transmitting ultrasonic energy to the tissue. Ultrasonic energy may also be used to arrest or minimize bleeding in tissue surrounding the surgical end-effector, causing hemostasis by coagulating blood or sealing vessels in the surrounding tissue.
Ultrasonic vibration is induced in the surgical end-effector by, for example, electrically exciting a transducer which may be constructed of one or more piezoelectric or magnetostrictive elements in the instrument handpiece. Vibrations generated by the transducer section are transmitted to the surgical end-effector via an ultrasonic waveguide which extends from the transducer section to the surgical end-effector.
In prior ultrasonic instruments, the waveguide of the instrument, through which ultrasonic energy is directed, is typically provided with one or more acoustic isolation elements which may be, for example, O-rings or other ring-like members. The acoustic isolation elements, which are positioned at vibratory nodes, acoustically damp the waveguide, thus preventing or reducing annoying or unwanted sounds. In addition, where the ultrasonic instrument includes an outer sheath, the acoustic isolation elements isolate the waveguide from the outer sheath. Such acoustic isolation elements are typically provided at one or more nodes of longitudinal vibration of the waveguide and are typically constructed of elastomeric material, such as silicone rubber. Acoustic isolation elements of this type are adapted to prevent loss of vibrational energy from the waveguide which can occur when the waveguide comes in contact with the outer sheath. Such contact can occur under side-loading or bending conditions, such as when force is applied to the surgical end-effector.
Acoustic isolation elements consisting of rubber O-rings are described in U.S. Pat. No. 5,449,370. Also described in U.S. Pat. No. 5,449,370 is the use of a polymeric sheath comprising protrusions formed of the polymeric material in contact with a waveguide, where the protrusions act as an acoustic isolation element between the waveguide and the sheath. U.S. Pat. No. 5,322,055 describes the use of acoustic isolation mounts positioned at nodes of ultrasonic vibration to avoid dampening or dissipation of desired energy transmission from a transducer to an end-effector. The acoustic isolation mounts described in U.S. Pat. No. 5,322,055 are not bonded to the outer sheath, facilitating the disassembly of the ultrasonic surgical instrument for subsequent cleaning.
Ultrasonic surgical instruments have been described which incorporate an acoustic isolating element which is also adapted to provide a seal. Such an arrangement is disclosed in U.S. patent application Ser. No. No. 08/949,161, filed Oct. 10, 1997, which was previously incorporated herein by reference. The device described in Ser. No. 08/949,161 includes an acoustic isolation element sealed to an acoustic waveguide, and in direct contact with an outer sheath or tube member, wherein the acoustic isolation element is positioned at the waveguide node closest to the distal end of the outer sheath.
Previously, acoustic isolation elements and acoustic isolation seals have been added to ultrasonic waveguides by, for example, injection molding silicone rubber onto the acoustic waveguides at vibratory nodes. Adhesion of the acoustic isolation element to the waveguide has been improved by the use of a primer material between the acoustic isolation element and the waveguide. When an outer sheath is positioned around a waveguide which includes an acoustic isolation seal, the acoustic isolation seal is compressed between the outer surface of the waveguide and the inner surface of the outer sheath. The compression fit of the acoustic isolation seal between the waveguide and the outer sheath creates a compression seal which is generally impervious to liquids or gasses when the instrument being used. However, such seals may allow liquid or steam to pass when the instrument is being sterilized by, for example, soaking or steam autoclaving. While this is generally not a problem for disposable instruments or instruments which can be disassembled before sterilizing, it may be a disadvantage in reusable instruments, particularly where the instrument cannot be disassembled prior to sterilization or where it would not be advantageous to disassemble the instrument before sterilization. Thus, during steam autoclave sterilization small amounts of steam may pass through the compression seal. Preventing fluids and steam from entering the space between the ultrasonic waveguide and the outer sheath is believed to enhance the useful life of reusable ultrasonic instruments.
It would, therefore, be advantageous to design an improved acoustic isolation seal which is substantially impervious to fluids and gasses, even during sterilization of the instrument. It would further be advantageous to form the acoustic isolation seal of a material which does not pass steam during sterilization. It would further be advantageous to provide an acoustic isolation seal which is substantially impervious to soaking or steam autoclave sterilization, thus sealing the instrument and preventing liquids or other contaminants from entering into the interior of the instrument. Furthermore, it would be advantageous to provide an acoustic isolation seal which is bonded to both the outer surface of the waveguide and the inner surface of the outer sheath of an ultrasonic surgical device, reducing the need for compression of the seal. Such an improved acoustic isolation seal would be particularly suited for use in reusable instruments such as those which are adapted for multiple patient use and are subjected to multiple sterilization cycles.